Voltage regulation.



E. O. SCHWEITZER. VOLTAGE REGULATION.

APPLICATION mm JULY 23.1914.

1,184,266. Patented May23,1916.

2 SHEETSSHEET l.

E. O. SCHWEITZER.

VOLTAGE REGULATION.

APPLICATION FILED JULY 23.1914.

1,184,266. Patented May23,1916.

2 SHEETS-SHEET 2- \A/IFE; In-van? Edmund Dfichwetlzef Jommm I E 5 znn,

EDMUND O. SCHWEITZER, OF CHICAGO, ILLINOIS.

VOLTAGE REGULATION.

Specification of Letters Patent.

Patented May 23, 1916.

Application filed July 23. 1914. Serial No. 852,629.

To all whom it may concern Be it known that I, EDMUND O. Sonwnrn acitizen of the United States, residing at Chicago, in the county of Cookand State of Illinois, have invented certain new and useful Improvementsin Voltage Regulation, of which the following is a full, clear, concise,and exact description, reference being had to the accompanying drawings,forming a part of this specification.

The subject matter of the present invention is a system of voltageregulation.

In. the consumption of electrical power it is often desirable to use theelectric current for different classes of service, that is, loads havingdifferent characteristics. A common illustration of the above is the useof induction motors for furnishing power and lamps for lighting purposeson the same premises. Economy of construction and installation woulddemand that both of these loads be fed from a single transformerinterposed between the power line and the consumption circuits, but itis well known that the characteristics of an induction motor, or otherinductive apparatus, for furnishing power or for similar purposes, areof a type entirely unsuitable for conjoint use with a noninductive loador a load of unstable characteristics such as a lamp load. Heretofore,it has been found impracticable to supply both loads with current fromthe same mains, due to the fact that voltage regulation of thecircuit'is impossible on account of the characteristics of the varyingload drawn by the motor.

It is one of the objects of the present invention to provide means whichwill allow of conjoint operation of an induction motor, or similar typeof apparatus, and a lamp load or other apparatus having a similarcharacteristic from a common supply circuit.

It is another object of the invention to provide a general method ofvoltage regulation in one branch of a split load circuit to prevent anyconsiderable voltage fluctuation, even when relatively great variationsof voltage occur in other branches.

It is a still further object of the invention to provide means forregulating automatically the voltage in one branch of a transformercircuit while a variable load is being drawn in another branch circuit.

The subject-matter of my invention iswidely applicable to varioussituations, and

may be embodied and practised in a great variety of forms.

I have illustrated in the accompanying drawings, in Figure 1, oneembodiment in which my invention may appear; Fig. 2 is a modification ofthe same; Fig. 3 is a diagram of a modification employing the windingsof the induction motor to secure regulation; Fig. 4 shows a modificationof F ig. 3; Fig. 5 is a diagram of a modification for obtainingautomatic regulation only upon the occurrence of excessively heavycurrent in the motor circuit.

In order to make clear the reason for employing my invention, I willbriefiy describe the characteristics of an induction motor and of a lampload.

The induction motor, as is well known, is, in fact, a tr: isformer, thesecondary of which is subject to motion at a speed depending uponvoltage as one factor. A decrease in voltage impressed upon the motorresults in ardecrease of voltage in the secondary or rotor winding, aconsequent diminution of the currenttherein accompanied by a decrease oftorque, and a consequent lessening of speed.

In .most situations in which an induction motor is employed, a variationin speed of a few per cent. is not found objectionable, inasmuch as theinduction motor is a variable speed device at best. A lamp load, on thecontrary, is almost entirely a resistance load but of an unstablecharacter. It is well known that the change of resistance, due toincrease of temperature, of an incandescent lamp, as well'as of an arclamp, tends to an inherent instability. Especially is this true of theincandescent light which is in common use in practically all situations.A variation of voltage upon an incandescent light affects the same veryunfavorably and a few per cent. voltage variation causes a very greatfluctuation in the value of the light given 05. Hence, when an inductionmotor is connected to lighting mains, the inductive effect of the motorcauses a fluctuation in the voltage of the circuits with a consequentflickering of the lamps. The current drawn by the motor causes aninductive and ohmic voltage drop in the connected winding of thetransformer and a decrease of voltage at the transformer terminals. As aconsequence, the voltage impressed upon the lamps is considerablydecreased and a very pronounced dimming occurs. This has been found soobjectionable that in practice prior to my invention it has beenimpossible to secure satisfactory service from such an installation.

In Fig. 1, I have indicated-the high tension or primary mains 1, 2,connected to the primary 3 of the transformer 1, the secondary 5 ofwhich is connected to the load by the leads (3, 7. The load illustratedin this connection consists of the induction motor 8 and a number oflamps 9 which may be of the are or incandescent or any other preferredtype. The induction motor 8 is bridged across the mains 6, 7, in serieswith a motor controller 10 which may be of any preferred type. In orderto secure regulation of the voltage across the lamps 9. I have insertedacurrent transformer 11 having a primary 12 connected in series with thelamp load and the secondary 13 connected in series with the inductionmotor 8. In order to regulate the value of the regulating eleetromotiveforce, which is induced in the primary 12, as will be explained further,I have connected an impedance 14in shunt of the primary winding 12. Theimpedance 1% is made practically pure resistance, for reasons which willbe set forth later.

The operation of the system above described will. now be explained.

Assuming that only the lamps 9 are con nected to the secondary of theload transformer, practically the only drop in the voltage in thecircuit 67 will be that caused by the current drawn by the lamps and maybe designated as a pure IR drop. This neglects. of course, the veryslight inductive effect in the impedance 14 and the winding 12 of thecurrent transformer 11. It is to be noted that the turns in the winding12 are of a low resistance, and comparatively few in number,consequently the IR drop caused in this part of the circuit will not beconsiderable. The current flowing in the winding 12 would induce anelectromotive. force in the secondary 13 which is in series with themotor, but, as this circuit is now open, no effect will -be producedthereby. Assume, as a second condition of the system, that the loadconsists of the motor 8; in this case the load is of an inductive typedue to the transformer and leakage effect in the motor 8, and aconsiderable drop of voltage at the terminals of the transformer 5 maybe occasioned, both by the inductive character of the winding 13 and theload 8 and by the IR drop, due to the resistance. of the circuitincluding the winding and the load. The secondary 13 of the transfornua-11 comprises a relatively large number of turns, and, consequently,includes more resistance than the winding 12, but, in view of the factthat the motor 8 is inherently a variable speed apparatus, a decrease inspeed, due to this drop of voltage, will not be objectionable, and may,if desired, be compensated for by manipulating the motor controller 10.It is to be noted that a voltage is generated at. this time in theprimary winding 12, but as the lamps are disconnected no current canflow therethrough. This voltage is of a low value, due to the relationof the number of turns. A current may circulate through the impedance 11 but this is a minor loss of power. However it is beneficial in effecttending to reduce the inductive action of the transformer 11, so thatcurrent can more readily flow theretln'ough. Assume as a third conditionof operation, that the motor 8 and the lamps 9 are connectedsimultaneously to the load transformer 1. The tendencies above describedfor each circuit are now combined into a single effect. The greater thecurrent drawn through the secondary 5 of the load transformer l, thegreater will be the drop of voltage across the terminals thereof. As aconsequence. the voltageimpressed upon both the motor 8 and the lamps 8)will be decreased. This is caused chiefly by the III drop. It will benoted that the current flowing through the secondary 13 of thetransformer 11 induces an electromotive force in the winding 12 which isshunted by the impedance 14. It is to be understood that there is aslittle inductance as possible in the impedance. Nearly pure resistanceis desirable in order to obtain the maximum effect. I have illustratedimpedance rather than pure resistance to show the art that the eilect isnot necessarily dependent upon pure resistance only, but may be gainedeven though there be appreciable inductance in the circuit. It is to benoted, however, that the en'lployment of an iron core in the impedance1:1- is highly undesirable, because the magnetization curve of iron isnot a straight line. As the permeability of iron varies at differentstages of magnetization, an iron core introduces complications whichcannot be compensated for. The electromotive force generated in thewinding 12 is considered separate and distinct from the voltage dropcaused by current flowing from the winding 5. This electromotive forcemay be considered as being impressed upon the shunt 14, tending to causea local current to flow therein. Hence, the added voltage which istransferred from the motor circuit may be considered as the IR dropacross the shunt 14, due to the circulating current that would flowbecause of the regulating voltage alone. If an inductance were shuntedacross the winding 12 the voltage added to the voltage of the winding 5would be due to both the electromotive force of the winding .12 and theinductive kick of the shunt. As a furx core'of the transformer 11 forproducing a somewhat similar effect. A number of taps 16 are led outfrom the winding 15 and an "adjustable contactor 17 is arranged to makeconnection with any one of these taps, so as to impress a variablevoltage upon the circuit 18, which is connected on one side to thewinding 15 and on the other to the contactor 17. A resistance isconnected in series with thecircuit 18, and the value of this resistance19 'may be controlled in any preferred manner, as by a rheostat arm 20to vary the resistance of the circuit 18, and the consequentshortcircuiting effect of the winding 15. In accordance with thewellknown action of the transformer, this variable' short-circuit actsas a shunt of greater or less value upon both the primary and secondarywindings of the transformer 11,

I and in this manner the regulating effect exerted upon the circuit ofthe lamps 9 may be varied to produce the most suitable effect.

The operation of the 'load circuits shown in Fig. 2 is similar to thatdescribed in connection with Fig. 1. The shunting means, which is shownin Fig. 1 as a direct shunt and in Fig. 2 as an inductive shunt,operates both' 'as an adjusting means for the voltage impressed upon thelamps and acts as well to .aidthe passage of current through thewindings 'of the current transformer 11 when each load circuit operatesalone.

In the diagram shown in Fig. 3, regulation is secured by placing anadditional ,winding 21 in inductive relation to the stator winding 20 ofthe induction motor 8. This winding 21 is connected in series with thelamp load 9 and corresponds with the winding 12 of Figs. 1 and 2. Inthismanner, it is possible to secure regulation without the use of anadditional transformer, as the iron of the induction motor may serveboth as the frame of the motor and as the core of a transformer forsecuring regulation. An inductance 22 and a resistance 23 are bridged inseries across the ter minals of the coil 21 and by manipulating thecontacts 24 it is possible to adjust the influence of the winding 21upon the lamp load circuit 9. It can readily be seen that theelectromotive force generated in the winding 21 is dependent upon theamount of current fiowing'in the stator winding 20.

In Fig. 4, instead of employing a direct shunt upon the winding 21, Ihave shown an additional winding 25 in inductive relation to the statorwinding 20 and in series with an inductance 22 and resistance 23, tosecure an adjustment of the electromotive force impressed upon thewinding 21 by means of an inductive shunt, this action being similar tothe inductive shunt 18 shown in Fig. 2.

In Fig. 5, I have shown a system in which the inductive effect of theregulating transformer 11 may be removed from the circuit, if sodesired, during the normal operation of the system. I accomplish this byshortcircuiting the winding 13 of the regulating transformer at alltimes, except when a heavy current is flowing through the inductionmotor 8, as in starting. This may be accomplished by the use of asolenoid switch having a winding 27 in series with the motor 8 andcontrolling by means of the bridge 28 the contacts 29, which areincluded in a short-circuit of the winding 13. It is desirable that theresistance of the short-circuit about the winding 13 be made of very lowvalue, but of considerable inductance. I have shown the inductance 26as'being connected in series with the contacts 29. The operation of thissystem is as follows: When the motor 8 is started, an excessive currentwill be drawn thereby, this current being traced in parallel through thewinding 13 of the transformer 11 and the short-circuit thereabout,through the windings 20 of the motor 8, solenoid 27, back to thesecondary 5 of the load transformer 4c. The current is sufficient tooperate the electromagnet c switch 28 and thereby open the short-circuitabout the winding 13 of the regulating transformer 11. As a consequence,the regulating electromotive force is generated uuring the time of theexcessive starting current. As. soon as the current in the motor 8becomes normal, the electromagnetic switch 28 is again closed and theinductance of the transformer 11 is thereby largely removed. This actionis practically instantaneous and regulation is not dependent entirelyupon the opening of the electromagnetic swltch 28, inasmuch as a suddenrise of current,

due to starting, is opposed by the inductance 26 to such an extent thata great part of .the 'circuit where such sacrifice is permissible.

The structures shown in the figures embody broadly a new method ofregulation. It can be seen that the voltage generated 1n the winding 12by a current fiowlng 1n the winding 13 is in proportion to the currentdrawn in the branch containing the motor 8, and may be made tocompensate to any degree for both the IR drop caused by such currentthrough the winding 5 of the load t'ansformer and may compensate, aswell, for the inductive effect caused by the fluctuations of the loadwhich would affect the lamps 9. This method may be more brieflydescribed as consisting of impressing an electromotive force upon onebranch of a transformer load circuit in accordance or in proportion, orin any desired relation, to the amount of current drawn by anotherbranch of the load circuit. The electromotive force so impressed has acomponent in phase with the electromotive force of the main loadtransformer winding and is varied to compensate both for the IR drop andfor the inductive effect which the variations in current in the secondbranch may cause in the load transformer winding.

It will be apparent to those skilled in the art that the invention maybe practised by the employment of different apparatus from what I haveshown and described but I consider the same to come within the spiritand scope of my invention. It is also not necessary that a load in theone branch consist of an induction motor, as any other type ofapparatus, which may be found suitable, and in which a low percentagedecrease in voltage will not be found objectionable, may be employed.But it is also evident that the other branch of a circuit need notnecessarily employ lamps or apparatus of a purely non-inductivecharacter, as any form of apparatus, which it is desired to maintain ata constant voltage, may be employed in this circuit. A greater number ofbranches may be employed as desired. It will also be ap parent that Imay employ an auto-transformer instead of a double winding transformershown in the figures of the drawing. It is important only that thewindings be arranged, as indicated, with a greater number of turns,which, in the drawings, I have designated as the primary winding of thecurrent transformer in series with the motor load and the winding offewer turns corresponding to the winding which I have designated as thesecondary winding of the current transformer in the lamp load. All ofthe above variations I consider to be fairly within the scope and spiritof my invention.

I consider my invention to be broadly new and desire the claims to beread as broadly as is consistent with the state of the art.

I claim:

1. In combination, feeder mains, a motor load branch and a lamp loadbranch having a variable number of lamps individually connected in pa'allel to said mains, an iron core, a winding on said core in serieswith said lamp branch, a winding on said core in series with said motorbranch, and a substantially non-inductive shunt for reducing theimpedance of said lamp branch winding when said motor load isdisconnected.

2. In combination a service t'ansformcr having a substantially constantvoltageimpressed thereupon, a motor load branch and a lamp load branchconnected in parallel to said transformer, said lamp branch comprising aplurality of constant voltage lamps adapted to be individually connectedin parallel, windings in series with each of said branches, a magneticcore interlinking said windings and a substantially non-inductive shuntconnected across the terminals of said lamp branch winding.

3. In combination a service t'ansformer having a substantially constantvoltage impressed thereupon, service mains, a motor load branchconnected .to said mains, said branch havingan induction motor connectedin series therewith, a lamp load branch connected in parallel in saidmotor branch, said lamp load branch comprising a plurality of lampsadapted to be individually connected in parallel, a magnetic core,windings on said core in series with each of said branches, and asubstantially non-inductive shunt connected across the terminals of thelamp branch winding.

In witness whereof, I hereunto subscribe my name this 13th day of July,A. D. 1914.

EDMUND O. SCHVVEITZER. Witnesses:

LESLIE IV. FRICKE, ERNEST IV. RAIALEE.

